At least 45% of the population in Dhaka city have developed antibody against Covid-19, finds the first-ever study on Covid-19 seroprevalence in Bangladesh.
The study by the Institute of Epidemiology, Disease Control and Research (IEDCR) and icddr,b also finds that the rate of Covid-19 antibody prevalence among slum people was a whopping 74%.
Presenting the study findings, lead researcher Dr Firdausi Qadri said the rate of antibody among people in Dhaka was "encouraging".
"It suggests the beginning of a herd immunity," said Dr Firdausi, a senior scientist at icddr,b, while revealing the findings at a programme at a city hotel on Monday.
Reaching the herd immunity threshold can play a great role in aiding recovery of the Covid-ravaged economy, particularly revamping the internal sectors, says Dr Selim Raihan, a professor of economics at Dhaka University.
"A large portion of low income people have already gone back to work. Either they were less aware or they ignored health risks because of the immediate needs. But their return to jobs helped the recovery of the manufacturing sector," he told The Business Standard when asked to comment on the survey findings about the herd community in Dhaka.
"The more people there are with Covid-19 antibodies, the faster will be the pace of economic rebound," said Prof Selim Raihan, also the executive director of South Asian Network on Economic Modeling (Sanem).
He, however, warned against over enthusiasm about herd immunity and stressed that the government needs to further expedite the initiatives taken to help the economy overcome the Covid-19 shocks.
"Otherwise, the recovery may take a longer time than expected," he said, referring to the rate of infections, which might reduce people's skills and productivity even after recovering from the disease.
The IEDCR-icddr,b study tested 553 symptomatic and 817 asymptomatic patients with IgG and IgM in 3,227 households in the capital. Besides, 96 symptomatic and 314 asymptomatic slum people were tested with the two types of antibodies in 960 households.
The IgM and IgG are the most useful for assessing antibody response, according to the Centres for Disease Control and Prevention in the US.
Dr Firdausi Qadri said the seroprevalence findings should not be mixed up with the prevalence rate of Covid-19.
"The prevalence rate might be higher," she said.
Replying to a question, she said the seroprevalence rate could not be used for predicting the second wave of infection.
"The antibodies are short-lasting, and we are hearing about second-time infections among some people," Dr Firdausi said.
Another study presented at the event found that 9.8% of the population in Dhaka city caught Covid-19, but the rate was 5.7% among slum people.
Replying to a question about higher antibody but low prevalence rate among slum people, Dr Firdausi said, "They are mostly asymptomatic, but it cannot be said that this population is less infected."
Another study on genomic epidemiology of Covid-19 in Bangladesh found that 19 distinct SARS-COV-2 lineages or descendants were circulating in the country. B.1.1, B.1.1.25, and B.1.36 were found to be the three main localised lineages in Bangladesh.
Lineages B.1.1 and B.1.1.25 spread to all eight divisions in the country, but B.1.36 was confined mostly to Chattogram division.
Lead researcher Tahmina Shirin, also the director of the IEDCR, said the study had found that Covid-19 was imported in Bangladesh in mid-February and the virus already spread all over the country by March.
She said the genomic data support multiple international importations of SARS-COV-2 from India, Saudi Arabia, the US, and the UK.
Commenting on the studies, IEDCR Principal Scientific Officer ASM Alamgir said sample sizes in the three studies were low and should not be accepted as the national prevalence.
But, he said, vaccination alongside antibody prevalence could help contain coronavirus in the country.
Presiding over the event, Directorate General of Health Services Additional Director General Meerjady Sabrina Flora said the studies would be carried out across the country.
She said no one was protected from coronavirus. "Wearing masks, washing hands, and maintaining social distance are crucial because no medicine or vaccine has been developed yet."
"We are talking about a second wave of infection, but we have to follow the health guidelines to prevent the spread of Covid-19," she added.
National Technical Advisory Committee on Covid-19 President Mohammad Shahidullah said the study findings could be used for making future plans.
Health Minister Zahid Maleque said Bangladesh did well in preparing against Covid-19 and that helped lower the severity of the virus.
Experts believe that herd immunity has developed in city slums.
Virologist Professor Dr Nazrul Islam said herd immunity develops when 70% people in a community get infected. Since 74% antibodies have been found in slums of Dhaka city, herd immunity has grown there. However, although the infection rate in slums is 5.6%, more research is needed to ascertain why antibodies are 74%.
Professor Nazrul, also a member of the National Technical Advisory Committee on Covid-19 said, the advantage of herd immunity is that if you grow hard immunity somewhere, the infection will not increase even if the infected people go there.
"This will reduce the pressure on the health system. As such, the slum dwellers are now in a somewhat advantageous position," he told The Business Standard, analyzing the impacts of the findings.
Dr M Mushtuq Hussain, Covid-19 pandemic control consultant to the Institute of Epidemiology Disease Control and Research (IEDCR) told The Business Standard, the prevalence of antibody in over 60% to 70% of the population it considered herd immunity.
Infection is less in slums as RT-PCR tests are less, he added.
Antibodies usually stay in the human body for three months, Dr Mushtuq pointed out, suggesting further research to see if antibodies still exist there.
A serosurvey carried out in three slums in Indian city of Mumbai suggests that 57 percent of the people in these areas developed antibody against SARS COV-2 in early July.
Sweden let Covid-19 spread in hopes the population would develop herd immunity. But the strategy failed eventually.
Herd immunity is a form of indirect protection from an infectious disease that occurs when a sufficient percentage--60 to 70 percent of a population has become immune to the infection, thereby reducing the likelihood of infection for individuals who lack immunity.